Bioinspired superficially mesoporous silica amorphous photonic crystals for humidity-responsive color switching

Inspired by the reversible color change of the beetle Tmesisternus isabellae in wet and dry environments, a humidity-responsive amorphous photonic crystals (APCs) film constructed with superficially mesoporous silica microspheres is prepared. The microspheres are synthesized via an etching and re-deposition process, and the APCs-based anti-counterfeiting patterns are fabricated by mask spraying. Upon introducing water vapor, APCs films exhibit a visible color transition from green to purplish-red. The shifts in the reflection peak are approximately 28–57 nm, depending on the thickness of the mesoporous shell. This color shift is clearly distinguishable by the naked eye and remains stable over at least 20 cycles. Meanwhile, APCs arrays composed of non-porous SiO₂ microspheres show negligible variation. Further studies indicate that the perfectly radially aligned mesopores within the porous shell may facilitate water vapor infiltration, leading to a fast, distinct, and reversible optical response. Our results show that encrypted patterns based on this material can be repeatedly revealed under dry and humid conditions, demonstrating strong potential for applications in reversible information encoding and decoding.